The invention discloses a device system and a method for washing chromium slags. The device system comprises a flocculant storage tank and a multi-stage washing device, wherein an end washing device of the multi-stage washing device comprises a pulping tank and a filter press, and the other washing devices separately comprise a pulping tank and a centrifuge; each centrifuge communicates with the flocculant storage tank and the corresponding pulping tank; the liquid phase outlet of the centrifuge of each stage of washing device communicates with the pulping tank in the previous-stage of washing device, and the solid phase outlet communicates with the pulping tank of a post-stage of washing device; the liquid phase outlet of the filter press communicates with the pulping tank of the previous-stage of washing device; the pulping tank of the end washing device communicates with the material inlet of the filter press; the chromium slags are added into the first-stage of washing device for pulping and then are pumped into the corresponding centrifuge; and the solid phase outlet of the filter press of the end washing device is connected to a chromium slag collection device. By adopting the device system and the method, continuous operation of chromium slag washing is realized; energy consumption is reduced; harmless treatment difficulty of the chromium slags is lowered; and the loss of a chromium belt is less than or equal to 0.5 ppm after chromium slag treatment.